Vitamin K Toxicity
Health professionals disagree on the optimal vitamin K dosage for the treatment of osteoporosis, cardiovascular disease and diabetes. But there are no known incidences of vitamin K toxicity from food or supplements.
The U.S. Food and Nutrition Board of the Institute of Medicine recommends vitamin K intake of 120 mcg/day for men and 90 mcg/day for women. The Board does not distinguish between vitamin K1 and vitamin K2 but this recommendation is generally thought to apply to vitamin K1 which is readily available in diets that contain dark leafy green vegetables.
Although these levels may be sufficient to ensure blood clotting and to support insulin regulation, research indicates that they are not optimal for cardiovascular and bone health. It is now believed that vitamin K2 provides the greatest benefit to heart and bone health... although this form of the vitamin is only 10% percent of total dietary vitamin K intake. (Rotterdam study, J Nutr. 2004 Nov;134(11):3100-5). Research has shown benefits from vitamin K2 in ranges as low as 32.7 mcg per day (which provided protection against heart disease in the Rotterdam study) to as high as 45 mg a day -the prescription dose of MK-4 used to treat osteoporosis.
Vitamin K appears to have a wide safety margin. There is no known toxicity associated with high doses of the vitamin and the United States had not established a Tolerable Upper Intake Level (UL). However, a synthetic form of vitamin K, vitamin K3 (menadione), is demonstrably toxic and has been banned by the FDA from over-the-counter supplements.People who are taking heart medications such as warfarin or coumadin are advised to take caution when using vitamin K supplements- as vitamin K2 is capable of blocking the blood thinning action of anticoagulants. This does not mean that the vitamin should be avoided completely as it also protects the heart from arterial calcification. Consulting with your doctor is always the best strategy to avoid vitamin K toxicity due to the interaction with prescription medications.
A year’s supply of 90 mcg Vitamin K2 (MK-7) will cost approximately $90.